1. Field of the Invention
The present invention relates to a linear actuator using a metal beam-type piezoelectric material, and an apparatus and a method for actuating the same.
2. Description of the Related Art
Piezoelectric actuators have the advantages of low noise, small number of components, compact bulk structure, high precision, stabilizing compensation, and precise control. Thus, piezoelectric actuators are used instead of conventional actuators in many areas. In particular, the use of piezoelectric actuators in the field of digital cameras and CCTV cameras and aerospace applications has grown rapidly. Additionally, piezoelectric actuators that generate a linear force without conversion from a rotation motion to linear motion such as those in a conventional DC or step motor are expected to be used in core technologies for future industries.
Conventional methods of generating a linear motion in a piezoelectric actuator can be classified into three methods.
First, a linear motion is generated in the piezoelectric actuator by using a rotation motion. The rotation motion is generated using friction between a rotator and a stator such as that in a conventional DC or step motor. Then, a linear force is generated using a thread of a shaft. The method of generating the linear motion is the same as a conventional method using a motor; however, because a rotation force is generated when a piezoelectric material is excited at an ultrasonic bandwidth using a property of the piezoelectric material, the method has important advantages such as low noise, high resolution, stabilizing compensation, and precision.
Second, a linear motion is generated by friction with a surface of an external object. In this method, surface portions of components of an object to move linearly make point contact with an actuator, and the object is moved linearly by friction. In this case, a surface of the object that is in point contact with the actuator has a predetermined hardness so as to withstand frequent friction caused by a high-frequency motion of the actuator. Moreover, additional components should be powered to stop or fix the object.
Third, a linear motion is generated using a bulk (single-layer, stack) type piezoelectric actuator by lifting an object linearly. In this case, there is no friction with an external object. To obtain a linear motion, an additional support needs to be installed. An example of a liner motion obtained using this method is the up and down linear motion of a helicoil. Because the motion is a bulk-type motion, the displacement is limited. Also, additional elements should be powered to stop and fix the object. Since the bulk structure includes a piezoelectric material, which is a kind of a dielectric material, and an electrode between piezoelectric layers serves as a capacitor, less power is required for stopping and fixing the object.
In the piezoelectric actuator using a rotation motion disclosed in Japanese Patent Publication No. 2003-181377, to obtain a linear motion from the rotation motion, additional mechanical elements are needed. That is, a shaft is installed on a spindle connected to a rotor of the piezoelectric actuator and interlocks with a thread of the object to move so that the object can move linearly. When the rotation motion is used without changes, power should be transmitted to the object to move while being engaged with a gear train or a thread of an object to be rotated. In addition, noise is generated when the mechanical components contact each other during the operation of the piezoelectric actuator.
In the piezoelectric actuator disclosed in U.S. Pat. No. 6,064,140, a linear motion is generated through surface friction between an external object and an object to move. Thus, the surface of the object should be specially coated or a material having great hardness should be used on the surface of the object so that when a power transmission tip of the piezoelectric actuator contacts the surface of the object, power is transmitted without any loss and the surface of the object is not damaged. In this case, due to additional processes for manufacturing the object, the manufacturing cost of the piezoelectric actuator increases, the manufacturing time increases, and due to the increase of weight of the object, other design parameters should be further considered.
In the bulk-type actuator disclosed in U.S. Pat. No. 6,512,321, the displacement of an object is limited because the displacement of the object is proportional to the stack structure of a piezoelectric portion of the actuator and the intensity of an applied electric field. That is, if you want to obtain a larger amount of displacement from the actuator, since the actuator should be designed by stacking more piezoelectric layers and a high voltage should be applied to the actuator, the size of the actuator increases, costs increase, and much power is consumed.